I have a 2000 360 mag that I rebuilt several years ago and the rebuild went bad, in a couple of ways, I don't want to get into "why" too deeply.
I will just say it involved a set of new "out of the box" EQ heads that definitely weren't "ready to run" as claimed. Had a couple of valve/piston collisions due to tight clearances. The break in oil came out a slurry of which I had never seen on a fresh rebuild before or since. It had a whole 6 miles on it when pulled. Freshly bored 0.030.

Anyway I may have a need for a 360 mag here and soon. But won't have to be a "hurry up to get running" deal, as were not "out" any daily drivers... might be adding one to the fleet that the present owner claims "needs engine". Looking at buying a. 03 Durango RT.

Anyway I'm afraid of reusing the pistons in the engine that I have here now //even though it only has a few hours on them since they were installed. Afraid because of the valve/piston collisions. Other than EQ heads this rebuild was stone stock including reusing the original cam

My son has a 360 LA that was likewise bored 30, and only had a few miles (like around 7500) before he decided he. Wanted "more" so re rebuilt that engine into a 408.
He has offered me those LA 360 pistons, they were speed pro/sealed power flat tops with only the 4 valve reliefs, they're hypereutectic coated pistons.
The intended use for this hypothetical build would be a tow pig/daily driver in a Durango. Watching the tach on the Durango we now own, (also a 360 magnum) I doubt this thing would see 3000 rpm very often, almost certainly not over 3500.
I know the balance factor on a LA vs a magnum is different but by how much? This would be the area of my greatest concern in using the pistons meant for an LA in a magnum block.

I'm wanting to see if I can build a decent engine staring with stuff I have on hand.
I also have an old but brand new "RT+10" cam I believe from the mid 90s.... how would that add into the mix given my intended usage? Currently just spit balling here.
I'm guessing I'm gonna need a set of heads to finish the build, not sure what I will want there. I have 1 good, stock, non cracked factory magnum head here, and 1 more that needs checked for cracks. Then 2 more stock magnum head candidates on the existing engine in the Durango I might be bringing home but not expecting those to be serviceable because of the claims the existing engine needs replaced due to overheating.

How about finding another 5.9? Very rarely need bored, save your bore job and pistons for something else. Probably gonna need cam and rod bearings, engine kits for these aren’t too bad.
Cam, intake and heads you will have to figure out but sounds like you have been down this road before. The china heads aren’t to bad and you’re left with a good 9.0-1 motor that came from the factory doing exactly what you’re asking for. There are loads of 5.9’s in the bone yard.

Beside the valves tagging the pistons, what damage is there to the current engine? Is it simply a matter of repairing the heads? I highly doubt the the valves hurt the pistons.
Doug

I bought another engine (used from CL) I took THOSE heads off, and they were (of course cracked. So I took my brand new supposedly ready to run EQ heads off the doomed overhaul, and had them redone// and properly clearanced, these heads are on the CL engine in my other Durango, the one the engine was rebuilt for in the 1st place.
And the doomed rebuild has been sitting on a stand in the garage since.
I wasn't wanting to get into all that happened with that doomed rebuild but since you're dragging it out of me, a long with the rebuild I had taken the injectors in for a sonic cleaning and rebuild at a local Bosch authorized fuel injection place and upon my maiden test drive the exhaust got red hot, glowing and melted down what was also a brand new magnaflow cat in the process. At least 1 of those injectors stuck wide open and washed down it's respective cylinder(s) hence the glittery slurry that came out with the initial oil change.
All I have for magnum heads is 1 known good, uncracked original. And 1 that needs disassembly and inspection. IF I bring this 2nd Durango home there is another set that could come apart for inspection and hope that at least 1 is uncracked of that pair.
The story I got on the Durango I'm going to look at is that it overheated, bad enough that their mechanic claims it n eds an engine and they were told it might be able to be machined and rebuilt. I haven't seen it yet, so far it is 2nd or 3rd hand info, I don't know their mechanic, for all I know maybe it just popped a head gasket. So the engine in that one might actually be ok. It remains to be checked out IF I wind up buying it.
Not saying anything bad about women and mechanical things/ I know some that would run circles around me/ but all I got was a story from the woman that listed it on marketplace, and she had to call her husband to jog her memory as to what the mechanic had told him/them. I asked her why they thought the engine needed replaced and she gave me a very short reply. "Pistons, cylinders radiator". Then later she came back with the story about what the mechanic said.

But regardless I would like to build this engine I have on hand using what I have here if possible. Those LA pistons I have, are the same oversized as the doomed 360 I have is, I could never figure out why every 360 I have ever had apart whether LA or magnum was cursed with dished pistons. I have this set of LA flat tops already, so I was really hoping that I could plug them in here and have it work with a power boost vs stock dished ones. But I'd rather ask and find out if someone else has done what I propose and whether it worked for them before I put an abomination together.
Where was the external balance mismatch at, between the LA vs the magnum version of the 360? Was it the crank, the rods or the pistons?

the china heads are garbage, filthy, flow worse than stock and frequently has tight guide clearances and I am guessing this is what he was sold as EQ heads possibly even by EQ since that is what they do now but the real EQ has not been sold in years.

those stock pistons can actually take a hit from the valves and keep going. Unless it is a big mess I would probably re-use them and not lose any sleep over them.

99% of magnum heads ae cracked yet it causes ZERO issues. The deepest crack I have ever seen in them was about 1/2 inch down but water is still another inch away, I would just run stock heads with cracks. I used to think it was an issue when trying to build one for my 68 dart back around 2000 when I worked at a dodge dealer so I bought a brand new pair not re-man and they were cracked right out of the box, if all these millions of trucks running around with cracked heads were billowing steam I might be worried but they don't so I never worried about them since.

I will tell you I have found about 6 total out of the hundreds I have had my hands on and every single on I have seen that was not cracked was from very early production and has a large 2 letters cast in near the spark plugs, if memory is correct FC, GX are generally the ones but they still crack a lot also just evidently less so than others.

I just double checked the un cracked pair I still have in my stash and it has a large GX cast there about 1/2 inch tall and very clear. The others in my stash that are cracked have a very small 2 letters cast in them around 1/4 inch tall and they are pretty blurry.

Problem is the machine shops I deal with won't do up a set of cracked heads. They tell me"they're cracked"and I never see them again.

Ok..even if those pistons that are on the engine that had the sticky valves are good .. ( I may end up re ringing those and using them yet. They don't have 3 hours on them from new. )
But for the sake of argument, (only I guess, at this point)
What would it hurt to use the flat top LA pistons that are only dished in the eyebrows for valve reliefs in a magnum block?

this was back in oct/nov of 2016. I think I wound up with 1 NZ head and 1, Chinamade head. I went right to EQs dock in chicago, and picked them up there. I got the last head off of 1 pallet and they un-shrink wrapped another pallet and I got the 1st one from that pallet. both boxes were marked the same. I read later (like a couple years) that they had a problem with them right around the time I had bought this particular set. Until then I didnt realize theyd switched to china. previous to that,I had bought a couple of sets of the original EQ heads and those were great. I wish I could get back one of those original sets I had.....

Hey guys I don't want to sound mean or anything but cant we just (or at least) answer on the feasibility of the LA pistons in the Magnum block? you guys seem to be ducking that issue,
If there is a true legitimate reason not to I would sure like to know.
I don't know yet if Im gonna get the durango this engine is being eyeballed for (yet) til I get down there and see the thing..... but I do want to do something (besides sell/scrap) the parts I have, staring me in the face.
I have what I have, plus another set of rods/mains, head gaskets, a couple of new oil pumps (one ea std and hi volume) plus the one in the doomed engine that was new less than 3 op. hours ago.... which I will probably open up, clean up and reuse.
will have to get another set of cam bearings and the rest of the gaskets, possibly another set of heads.
Roller lifters in doomed engine were also brand new with rebuild. will probably keep those in there too.
once we get past the piston question, then well get into heads, cam etc.

at one point i had heard that if you got a set from a 318 they would be less likely to be cracked than a set (yeah I know--- same casting numbers) off a 360.

The 1995 Ram Pickup FSM has a mistake in that the FSM picture of the Magnum 5.9 Piston is wrongly the last of the TBI LA 360 pistons.
Those LA pistons have a round cavity crown dish, and are heavier.

The correct 1993-1995 Magnum 5.9 pistons are shown in the 1995 FSM as a drawing in the iron V10 section of the FSM.
Those new Magnum pistons have a “soapdish” cavity in the crown of the piston to create “tumble air motion” and the pistons are lighter weight.

To use oversize bore LA pistons in the Magnum engine will change the static compression ratio and throw the engine balance off.

Since it is externally balanced in theory you could collect all the numbers and change those external weights without having a machine shop spin the new combination of parts.

Be aware of some years Magnum engine external weights changing from on the flexplate to on the Torque Converter - and check for a change of part number on the torsional damper, as the external weight at the front of the engine matters too.

It is my guess that the latter year Magnum Cylinder heads crack because somehow the “induction hardening” of the valve seats did not get a long enough “tempering time” in an oven. Shortening the tempering time speeds up the production line.
An alternate guess would be that someone changed the alloy chemicals in the cast iron to a cheaper mix.

Larry Shepard may have admitted this in his article about the aluminum Magnum heads.
Someone at Chrysler convinced E’booger to search out aluminum Magnum heads for his Dakota pickup build.

Yeah I know the difference in shape of the tops of LA vs magnum 360 pistons. My question remains (I've been asking this for years with no answer. WHY do all 360s come with dished pistons?
I think it simply castrates them, of all that sing the praises of the 360, the 360 could be so much better than it ever was if it didn't have that handicap. In my experience (though I've never had the luxury of racing) I've never had a 360 that would do what a 318 supposedly wouldn't.
I have these 360 mags here, my Durango (along with the 2nd durango I'm looking at) originally came with 360s (of which I think are far superior to 4.7s which by these years was the only other engine choice in a Durango)
And yes I know about the "some had the weight on the converter while others had it on the flex plate".

I heard this too. Rationale was 5.9l mag motors were run hotter to meet emission targets. Don't know if it's true, but it stands to reason.

lol, same thermostats, not sure how it's run hotter.

Maybe more EGR than a 5.2? But that usually knocks down the peak combustion chamber temps for NOX control. Maybe the 5.2 runs more EGR?

I suspect this is an urban myth

Yip, I’ve ran cracked heads even on claimer circletrack motors, back then you had no choice except hunt for other probably cracked heads. The eq heads were good. Did the op buy these heads assembled from eq? Eric I think would have stood behind them. The china ones are nothing like the old one BUT, For a stockish build they are ok, they have inserts for both intake and exhaust, use them on propane motors with good results. I don’t trust any preassembled anything anymore. Guess you will have to figure it out.
Sorry to run off the topic again.

I have wondered pretty much the same.

The flat top of Magnum 5.2 pistons would seem to be better to “quench” up close to Magnum Cylinder head combustion chambers in order to shoot inward “squishes of gas” to create a “fast burn,” right?

The 360 ‘s have dished pistons because Chrysler did not want to have the expense of a custom cylinder head just for the 360 ci/5.9L

The “correct” cylinder head for a Magnum 5.9L V8 would have a combustion chamber roughly 11 cc’s bigger so there would not be a 11 cc dish in the 1994-1995 pistons, at least in my “guess-ti-mation.”

Willem Weertman tells us in his book “Chrysler Engines” that Magnum 5.9 pistons were designed to be used in truck iron V10 engines as well to “cut costs.”

Willem Weertman might have the knowledge that “actually the soapdish in the 5.9L piston crown reduced NOx emissions a useful amount.”

NOx emissions troubled the 1994 5.2 Magnum because Chrysler “choked down” Magnum design exhaust manifold inside diameter to force greater EGR flow through increased exhaust back pressure. Today, 1992-1993 5.2 Magnum exhaust manifolds bring a premium price.

It is not wrong to think that in the best case
the crown of any piston should be matched to the combustion chamber of the cylinder head above.

If this subject interests you read up on
ex-Porsche engine designer Michael May’s contract work for
British Jaguar that created the “May Fireball” combustion chamber used for a few years in the Jag V12.

swirl, squish, quench, tumble
all those came from motorcycle engine racing “tweaks”

Except they did have 360 specific heads. You'd see those same heads on a 4bbl 318, but the 2bbl 318's had different heads.

So much for that theory.

The reason the 360 had dished pistons was for emissions purposes, lower compression helped them pass the emissions back then. Now days, that isn't as applicable.

You could run the closed chamber 2bbl 318 heads on a 360, btdt. The torque increase was noticeable. But the top end suffered due to the small ports. IF the large port open chambered 360 heads had the 318 2bbl closed chambers that would have been the best of both worlds.

you can do it but it needs balanced. I did it once, actually in the same 68 dart and it vibrated a lot so I had to pull it back apart for balancing and it was not at all a high RPM engine.

The huge dish and pistons deep in the cylinder on an LA but still on Magnums was to reduce NOX emissions.

There are several possibilities for the "318 magnum crack less than 360 magnum theory", first of all those early castings I mentioned were more often found on 318s because well they made em an extra year VS 5.9 mag production. That good pair I have in my stash came from a 300,000 mile 92 318 mag. Second reason I can think of is that the 5.9 magnums got the "death flash" witch was basically very retarded ignition timing to keep spark knock down and this results in hotter exhaust temp because it didn't burn as completely before the ex valve opened.

Couple things that leads me to think it was just they way they were made is the fact it is almost always the two end cylinders and almost never the center cylinders, they should have all 4 had basically the same tune, the rear cylinders got much cooler air than the front cylinders because of the hot water passage heating up the air in the front runners in the beer keg so in theory the rear should not have cracked as much or the cracking would have been worst in the front and progressively less as it went back but it didn't and mostly I just decided it was just the way they were made after I bought a brand new pair that were cracked right out of the mopar box.

Most likely it all added up together so even if a pair was not cracked new they soon cracked because of the other conditions but again no issues ever in my experience. If your machine shop won't do a valve job ask em to do it with no warranty, if they say no take em somewhere else.

On your particular heads a quick pic of the ends and I can tell very easy if they are chinese or new zealand casting...

The 360 never really had a head designed just for it, the LA 360 used heads made originally for the 340, the magnum 5.9 used heads that were first used on magnum 5.2s... both basic varieties ever used on 360s were used for other engines first, sure there were specific casting numbers that only ever came on 360s but they were just insignificant revisions on the 340 head. The closest thing to a 360 specific head was the 308 but it was still just a minor update on the 340 head to accommodate a roller cam (bigger pushrod hole that pinched the port even more) with a slightly improved ex port, it was very short lived and cracked in ways that made it un-useable a lot of the time.